Abstract
Measurements have been made in the wake of a model wind turbine in both a neutral and a stable atmospheric boundary layer, in the EnFlo stratified-flow wind tunnel, between 0.5 and 10 rotor diameters from the turbine, as part of an investigation of wakes in offshore winds. In the stable case the velocity deficit decreased more slowly than in the neutral case, partly because the boundary-layer turbulence levels are lower and the consequentially reduced level of mixing, an ‘indirect’ effect of stratification. A correlation for velocity deficit showed the effect of stratification to be the same over the whole of the measured extent, following a polynomial form from about five diameters. After about this distance (for the present stratification) the vertical growth of the wake became almost completely suppressed, though with an increased lateral growth; the wake in effect became ‘squashed’, with peaks of quantities occurring at a lower height, a ‘direct’ effect of stratification. Generally, the Reynolds stresses were lower in magnitude, though the effect of stratification was larger in the streamwise fluctuation than on the vertical fluctuations. The vertical heat flux did not change much from the undisturbed level in the first part of the wake, but became much larger in the later part, from about five diameters onwards, and exceeded the surface level at a point above hub height.
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Notes
In the discussion, the terms ‘undisturbed’ and ‘upstream’ are taken as synonymous.
As in wind-tunnel settling chamber screens, for example.
References
Chamorro LP, Porté-Agel F (2010) Effects of thermal stability and incoming boundary layer flow characteristics on wind turbine wakes: a wind tunnel study. Boundary-Layer Meteorol 136:515–533
Fuglsang P, Bak C (2004) Development of the Risø wind turbine airfoils. Wind Energy 7:145–162
Hancock PE, Pascheke F (2013) Wind-tunnel simulations of the wakes of large wind turbines: Part 1, the boundary-layer simulation. Boundary-Layer Meteorol (this issue)
Hassan U (1993) A wind tunnel investigation of the wake structure within small wind farms. Energy Technology Support Unit, UK, report ETSU WN 5113, 204 204 pp
Laitone EV (1997) Wind tunnel tests of wings at Reynolds numbers below 70000. Exp Fluids 23:405–409
Lu H, Porté-Agel F (2011) Large-eddy simulation of a very large wind farm in a stable atmospheric boundary layer. Phys Fluids 23:065101
Magnusson M (1999) Near-wake behaviour of wind turbines. J Wind Eng Ind Aerodyn 80:147–167
Magnusson M, Smedman A-S (1994) Influence of atmospheric stability on wind turbine wakes. J Wind Eng 18:139–152
Magnusson M, Smedman A-S (1999) Near-wake behaviour of wind turbines. J Wind Eng Ind Aerodyn 80:169–189
Scorer RS (1967) Causes and consequences of standing waves. In: Reiterand ER, Rasmussen JL (eds) Proceedings of the Symposium on Mountain Meteorology: Colorado State University. Atmospheric Science Paper 122
Sunada S, Sakaguchi A, Kawachi K (1997) Airfoil section characteristics at a low Reynolds number. ASME J Fluids Eng 119:129–135
Townsend AA (1976) The structure of turbulent shear flow. Cambridge University Press, Cambridge, UK, 450 pp
Acknowledgments
The work reported here was performed under SUPERGEN-Wind Phase 1, Engineering and Physical Sciences Research Council reference EP/D024566/1. Further details can be found from www.supergenwind.org.uk. The authors are particularly grateful to Mr T. Lawton and Dr P. Hayden for their assistance in setting up the experiments, to Prof. A. G. Robins for useful discussions, and to Mr A. Wells M.B.E. for making the model turbines. The EnFlo wind tunnel is a Natural Environment Research Council/National Centre for Atmospheric Sciences national facility, and the authors are also grateful to NCAS for the support provided.
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Hancock, P.E., Pascheke, F. Wind-Tunnel Simulation of the Wake of a Large Wind Turbine in a Stable Boundary Layer: Part 2, the Wake Flow. Boundary-Layer Meteorol 151, 23–37 (2014). https://doi.org/10.1007/s10546-013-9887-x
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DOI: https://doi.org/10.1007/s10546-013-9887-x